During an interview on 6abc, Erickson said: "From what I understand, it was someone who did not work there that was having a confrontation with their significant other."

Erickson said she knew something was wrong as soon as the facility was being evacuated.

"Then there was a massive police presence as soon as we were walking out of the building, there were a good ten cop cars, they all had their guns drawn out heading toward the main entrance of the building," Erickson said.

"I noticed people running out the back exit and I asked a coworker 'why is everyone running outside?' Next thing you know I hear a gunshot and a coworker screaming 'Everybody get out, he's got a gun,'" Harden said.

Support is being offered for employees who witnessed the terrifying and dramatic standoff.

In a statement issued after the incident ended, UPS said:

"UPS greatly appreciates the work of the law enforcement personnel who responded to this morning's active shooter situation at the company's supply chain processing facilities in Logan Township, New Jersey. The incident is concluded and all of the employees are accounted for and being attended to by local officials. Support services for employees who work at the site will be provided as they recover from this unfortunate incident."